Process of simultaneously producing calcium metal and a silicon-aluminum alloy



' process under vacuum from lime.

United States PatentC PROCESS OF SIMULTANEOUS LY PRODUCING CALCIUNIMETAL AND A SILICON-ALUMI- NUNI ALLOY Jean Lucien Andricux and EtienneBonnier, Grenoble, France No Drawing. Application September 20, 1956Serial No. 610,902

Claims priority, application France October 5, 1955 3 Claims. (CI.75-67) The present invention relates to the simultaneous prep+ arationof calcium metal and a silicon-aluminum alloy.

Calcium metal is generally obtained by an electrolytic process fromcalcium chloride or by an aluminothermic Silicon-aluminum al-, loy isgenerally prepared by an electrothermic process.

The above processes of manufacture of calcium all give defective yields,the electrolytic process owing to the metal losses, in particular, bydissolving in the bath, and the aluminothermic process owing to thenecessary form: ing of a slag of lime aluminatef It is possible, bydistillation under vacuum, to separate the constituents of metal alloys,as far as these constituents form a true solution at the temperature ofthe operation and have sufficiently different vapor pressures.

It is known that the presence of strong intermetallic affinities limitsthe yield of such separations by distillation.

.It is known, also, that in the case of strong inter: metallicafiinities impeding the separation of the constituents of an alloy, itis'possible to displace favorably the equilibrium of dissociation of thedefinite compounds by introducing a third element presenting for one ofthe constituents a greater affinity than that which it reveals, at thetemperature in question, for the other.

As regard the AlCa and SiCa alloys, the vapor pressures of aluminum andsilicon are substantially lower at any temperature than that of calcium.This would allow to foresee a possible separation of the calcium fromthe other elements of these alloys. However, each of these systems, AlCaand SiCa, presents, besides definite compounds which are unstable at atemperature above 1000 (3., compounds stable at a higher temperature,which are respectively CaAl and CaSi. Theheat of formation of thesedefinite compounds ishigh and shows the strength of the afiinitiesbetween A1 and Ca on the one hand and Si and Ca on the other hand. Thissituation limits the abovefconsidered possibilities of separating Cafrom Al and Si to only the elements which are free in the alloy.

At last the Al-Si system presents no compounds but, only, in the liquidstate, a continuous zone of solution of 0 to 100% of each of theconstituents. Then it is not possible to think of an effectualdisplacing of equilibrium of Ca from Al or Si by the addition of one orthe other of the metals Al or Si used alone.

The present invention allows one to overcome these diificulties. Itcomprises heating at a temperature of from 1300" to 1400 C. under areduced pressure of from 0.1 to 1 micron of mercury a mixture of twoalloys (aluminum-calcium alloy and silicon-calcium alloy) in judiciouslycalculated proportions and collecting the calcium metal which distillson a cooled condenser; der the conditions which will be indicatedfurther, the non-vaporized molten residue is then composed of asilicon-aluminum alloy containing very little calcium.

It is preferred to use as raw material, on the one hand,

2,867,527 en e Ji 6 2 the aluminum-calcium alloys which are obtained bythe process of aluminothermic reduction of lime at normal pressure andwhose calcium content can reach 25% in weight and, on the other hand,the electrothermic siliconcalcium alloys whose content is near 30 to 33%calcium.

These latter alloys may be obtained, for example, by reduction of silicaby carbon and calcium carbide or, also, by reduction of lime bysilicon-aluminum alloys.

'But it is possible in order to improve the production of calcium metalto start with alloys richer in calcium, such as those which it ispossible to obtain by the electrolytic method from lime aluminates andsilicates.

Anyway, it is thus possible to extract with an excellent yield thecalcium contained in the alloys of this metal with aluminum and silicon.i I I The operation may be carried out as follows.

The charge, suitably crushed to the size grain of wheat, is intimatelymixed and placed in a refractory crucible which is introduced into adistillation furnace. The pressurebeing reduced to a pressure of 0.1 to1 micron of mercury, the furnace is filled with argon from whichnitrogen has been carefully cleared and the argon is then removed fromthe furnace. One proceeds afterwards to the heating while maintainingthe reducedpressure in order to ensure the removal of gas fromthemetallic mass, chiefly from the AlCa alloy. wiinjs'iemperature of 1320to 1350 C. has beeiire'achedgfbr an interior pressure of about 0.3 to0.1 micron of mercury, this state is maintained during a time determinedac; cording to the weight of the mass to be treated and to thesuperficial dimensions of-the liquid metallic bath. For example, when arefractory crucible containing a mass of 50 g. of mixture is used, onehour is enough to carry out the operation, The heating is afterwardsstopped and, when the furnace is sufliciently cool, argon is in-,troduced until an interior pressure equal to the outer pressure isobtained. The furnace can then be opened and the condenser removed. Thecondenser retains the calcium deposited according to the basalticstructure peculiar to distilled calcium.

The weight of metal collected. on the condenser, its calcium content,the. weight of molten residnereinaining in the crucible and it calciumcontentallow one to calculate the yield of calcium. Under the indicatedconditions, it is between 95 and generallyabout 97%. t

' The metal collected on the condenser always contains a little aluminumin proportions comparable'with those present in aluminothermic-producedcalcium obtained under vacuum. The silicon content on the other hand isveryllowas indicated by the examples given hereafter. The contaminationof the calcium by aluminum increases with the temperature employed and.may be minimized by a lowering of the temperature but this lowers theyield of calcium.

According to economic conditions, it is possible to vary within greatlimits the relative ratios of the AlCa and Si-Ca alloys so as to extractas much calcium metal as possible from the less expensive raw material.

The advantage presented by the process according to the invention are asfollows:

(1) A great part of the extracted calcium comes from electrothermicsilicon-calcium alloy easy to obtain and generally less expensive thanthe aluminum-calcium alloy.

(2) The aluminothermic reduction of lime at ordinary pressure and thefurther distillation under reduced pressure of the obtained alloy aremore economical than the operation of aluminothermic reduction of limeunder reduced pressure because the yield of the operation carried out onthe aluminum-calcium alloy under reduced pressure is near 100% and isnot limited by the formation of slag which in the aluminothermicprocess. of reducing lime retains nearly 60% of the introduced calciumand aluminum. The aluminothermic reduction of lime with a low yield iscarried out in a rudimentary apparatus as large as desired. It is, onthe other hand, very expensive and often impossible to build largefurnaces with a much reduced pressure.

(3) The residue of the operation is a silicon-aluminum alloy of highcommercial value, utilizable for the preparation of light foundry alloysof the Alpax type, whereas the aluminocalcic slag collected in theprocess of direct reduction under vacuum of lime by aluminum is, on theone hand, a worthless residue and, on the other hand, a hindrance tocarrying out the process, in particular, on account of the destructionof the working crucibles.

,In order that the invention may be more clearly understood, twoexamples of carrying out the process according to the invention aregiven below.

Example 1 The composition and the origin of the basic raw materials areas follows:

(1) Aluminothermic aluminum-calcium alloy with a Ca metal content of17.0i0.3%.

(2) Electrothermic silicon-calcium alloy with a Ca metal content of30.5:0.5%.

Composition of the charge- Al-Ca alloy 64% Si-Ca alloy 36% Weight of thecharge 50 g. Distillation temperature 1320 C. Distillation pressure 0.20micron of mercury. Time required for the distillation 1 hour.

The weights and compositions of the obtained products were as follows:

1. Condensate of calcium g 10.5

Contents in elements other than calcium- Si percent 0.17

A1 do 1.60

2. Residue of silicon-aluminum alloy g 38.5 a-eo entf this alloyCapercent 1.12

The content of aluminum in the so densate of calcium can be lowered byincreasing the proportio Yield of calm of silicon-calcium alloy in thecharge as in the followf ing example.

4 Weight and composition of the obtained products 1. Condensate ofcalcium 10 g. Contents in elements other than Ca Si "percent; 0.53 A1 do1.1 2. Residue of silicon-aluminum alloy g 38 ,Ca content of this alloyCa "percent" 5.20

Yield of calcium do 84 By increasing still more the silicon-calciumalloy rato in the charge, the aluminum content of the distilled calciumlowers still more but its silicon content increases and the extractionrate lowers. For instance, if the charge is composed of 13% Al'-Ca alloyand 87% Si-Ca alloy, the obtained calcium contains 1.75% Si and 0.93% Aland the yield ofcalcium is lowered to 69%.

The composition of the silicon-aluminum alloy obtained as residue of thedistillation depends, of course, on the proportions of the AlCa andSi-Ca alloys in the charge.

The invention is not limited to the preferred embodiment but may beotherwise embodied or practiced within the scope of the followingclaims.

We claim: v

1. A process of simultaneously producing calcium metal and asilicon-aluminum alloy,.which comprises v heating a mixture ofaluminum-calcium alloy and silicon calcium alloy in an inert atmosphereat a temperature of 13001400 C. at a pressure of 0.1 to 1 micron of 2. Aprocess according to claim 1, wherein the aluminum-calcium alloyemployed is produced by the alumi nothermic reduction of lime 'at normalpressure and contains up to 25% by weight of calcium.

3. A process according to claim 1,. wherein the silicon-calcium alloyemployed is produced by the reduction of silica by carbon and calciumcarbide and contains about 30% by weight of silicon.

References Cited in the file of this patent UNITED STATES PATENTS1,607,245 Duhme Nov. 16, 1926 1,728,942 Marden Sept. 24, 1929 2,194,965Andrieux Mar. 29, 1940 7.298 Dean .4 Dec. 23, 1941 2,362,147 MondolfoNov. 7, 1944 2,425,705 Tetu Aug. 12, 1947 2,464,767 Pidgeon et al. Mar.15, 1949 2,513,339 Loevenstein July'4, 1950 2,684,898 Barton, July 27,1954 FOREIGN PATENTS 2,270,060 Great Britain May 5, 1927

1. A PROCESS OF SIMULTANEOUSLY PRODUCING CALCIUM METAL AND ASILICON-ALUMINUM ALLOY, WHICH COMPRISES HEATING A MIXTURE OFALUMINUM-CALCIUM ALLOY AND SILICONCALCIUM ALLOY IN AN INERT ATMOSPHEREAT A TEMPERATURE OF 1300-1400* C. AT A PRESSURE OF 0.1 TO 1 MICRON OFMERCURY TO DISTILL OFF CALCIUM AND PRODUCE A MOLTEN RESIDUE OFSILICON-ALUMINUM ALLOY, CONDENSING AND RECOVERING THE CALCIUM, ANDRECOVERING THE SILICON-ALUMINUM ALLOY.